1. Field of the Invention
The present invention relates to a reciprocating apparatus, a method of controlling a reciprocating apparatus, and an injection molding apparatus, each able to thrust, for example, the push-pin provided in a mold, precisely to the preset position and to reciprocate the push-pin at high speed a prescribed number of times.
2. Description of the Related Art
An injection molding apparatus comprises an injection device and a mold fastening device. The injection device has a cylinder and a screw provided in the cylinder. The mold fastening device is designed to open and close a mold. In the cylinder of the injection device, the screw is rotated and moved back and forth, injecting molten resin into the mold in order to form a product.
The mold fastening device comprises a mold fastening mechanism and a pushing mechanism. The mold fastening mechanism can first open and close a mold and then fasten the mold, in order to form a product. The pushing mechanism is configured to push the product out of the mold. The pushing mechanism has, in most cases, a drive mechanism and a push-plate. The drive mechanism can reciprocate the push-plate. The push-plate can abut on a push-pin provided in the mold. Hence, the pushing mechanism can be coupled to the push-pin.
After the mold fastening device has opened the mold, the pushing mechanism is driven. As a result, the push-plate pushes the push-pin from the mold. The product is thereby pushed out of the mold and made to fall into, for example, a product collecting box. As is known in the art, most pushing mechanisms developed in recent years have an electric motor, particularly a servomotor, which drives the push-plate.
It is desired that the time for molding the product should be shortened in the injection molding. In view of this, a technique of moving the push-pin (pushing member) at high speed has been developed (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-286857). This technique is a method of controlling the ejector of the injection molding apparatus. In this method, the position of the push-pin is accurately controlled only in the step of moving back the push-pin. In any other step, the push-pin is never stopped at the foremost position and the pushing member is moved faster than in the step of moving back the push-pin. Since the push-pin is not accurately positioned, except in the step of moving back the push-pin, the push-pin can be moved at a higher speed than before.
The injection molding apparatus forms not only products that can be made even if the push-pin is not accurately positioned, but also products that cannot be made without accurately positioning the push-pin. The technique described above (i.e., moving the pushing member at high speed) can indeed be used even if the push-pin is pushed to various positions to make products, but cannot be used if the push-pin should be pushed to the precise position preset to make products.
Further, it is demanded that the push-pin should be reciprocated at high speed and be precisely controlled in position, to mold a product, thereby to shorten the time for molding the product.